for National Geographic News
Stevie Wonder may have been on to something when he sang about a ribbon in the sky.
In a discovery that took astronomers by surprise, the first full-sky map of the solar system's edge—more than 9 billion miles (15 billion kilometers) away—has revealed a bright "ribbon" of atoms called ENAs.
The solar system is surrounded by a protective "bubble" called the heliosphere.
The narrow ribbon snakes along this bubble's inner wall between Voyager 1 and 2, twin spacecraft that have been exploring the solar system's boundary since 2004 and 2007, respectively. (Related: "Voyager Probes Send Surprises From Solar System's Edge.")
Voyager data, taken from specific regions within the boundary zone, had offered no hint that the ribbon existed. But from its orbit around Earth, NASA's Interstellar Boundary Explorer, or IBEX, spacecraft was able to give researchers a wider view.
IBEX team member Eric Christian, of NASA's Goddard Space Flight Center, compared the Voyager spacecraft to weather stations on Earth.
"Can you imagine trying to determine the weather of the entire Earth from two weather stations? You can't do it," Christian told reporters at a press conference this afternoon.
"IBEX is like our first weather satellite, and it gives us the full picture [of the heliosphere]."
IBEX's map shows that the ribbon measures roughly two billion miles (three billion kilometers) long and several hundred thousand miles wide.
The ribbon isn't visible to people and wouldn't harm spacecraft or humans passing through it, IBEX principal investigator David McComas, of the Southwest Research Institute in Texas, told National Geographic News.
Astronomers aren't yet sure how the ribbon formed, but it's possible that the ribbon could be a result of pressure exerted on the heliosphere by our home galaxy's magnetic field.
Particle Crashes Seed Solar System Ribbon?
Since its launch almost a year ago, IBEX has been detecting the ENAs (energetic neutral atoms), atoms that have been stripped of their electric charges.
ENAs are created at the outer edges of the heliosphere, which is formed by solar wind—charged particles streaming rapidly outward in all directions from the sun.
Some gases from outside the heliosphere are constantly leaking in, and when the fast-moving solar wind meets these slow-moving gases, ENAs are born.
At the moment of their creation, some of these ENAs get shot toward Earth, where IBEX's sensors eventually detect them.
"We've observed about a million ENAs over the six months that it took to make the sky map," McComas said.
Ribbon a Sign of Heliosphere Being Squeezed?
The ENA ribbon's existence suggests the atoms are produced in higher densities in some parts of the outer heliosphere than others, McComas said, although scientists aren't yet sure why that would be the case.
One idea is that, wherever the Milky Way's magnetic field presses on the heliosphere, more ENAs are created.
"Exactly where the [galaxy's] magnetic field is most wrapped around the outer boundary of the heliosphere, that's where the ribbon runs," McComas said.
"That could be an unbelievably remarkable coincidence, or it could be a fabulous clue that somehow this external magnetic field is actually imprinting onto our heliosphere through some process that we don't yet understand."
The team is currently putting together the second IBEX sky map of the heliosphere, and there are already indications that the ribbon's shape is changing, McComas said.
"There's some suggestion," he said "that it's actually slightly different and maybe evolving over the 6 months since the [first sky map]."
Findings detailed in this week's issue of the journal Science.
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